Radar and other active range determination systems are in widespread use for military, commercial and private purposes. Radar systems have well-known characteristics, in that long-range detection of small objects is known to require transmission of more power, higher gain antennas, and/or more sensitive receivers than that or those required for short-range detection of large objects. Tightly spaced objects, i.e. clusters, of similar size are most difficult to resolve accurately. The resolution of images of closely spaced clusters, particularly those residing off of the ambiguity ridge due to the application of a linear frequency modulated (LFM) waveform, is particularly difficult. LFM pulses are commonly used as radar pulses.
Some conventional range ambiguity resolution techniques require transmission of additional signals with additional dwells for resolving the range interval of the ambiguous object. The additional dwells or transmissions consume additional radar resources, undesirably resulting in a greater overall time required for completion of a surveillance scan.
The generation of range-Doppler images in radar systems has been known and found to be useful for processing continuously collected radar data into an image, but even with range-Doppler images, it remains difficult to resolve the individual scatters associated with closely placed clusters, even for those residing off the ambiguity ridge, due to the application of a LFM pulse that spreads the associated waveform in range and Doppler space.
Range-Doppler and other images typically used in radar are conventionally pre-processed in terms of analog manipulation of the image and such is a limitation, i.e. shortcoming, with respect to how well the radar image can be easily and conveniently manipulated and with respect to the quality of the resolution of multiple clusters, especially closely spaced clusters of similar size. Conventionally, the analog signal amplitude and sensitivity are compromised.
One prior attempt to improve the resolution of closely spaced clusters includes increasing the detection threshold but accompanying this approach is an artificial loss in gain as previous minimal detections fall below the increased threshold level. FIGS. 1A and 1B illustrate this shortcoming of the prior art. In FIG. 1A, detection threshold 2 is comparatively low and small object 4 is detected, i.e. lies above detection threshold 2. Closely spaced objects 6 and 8, however, are unresolved. In FIG. 1B, a higher detection threshold 10 is employed aiding in the resolution of objects 6 and 8. Small object 4, however, is below the detection threshold and is therefore undetected.
It would be desirable to provide a system and method for improving the resolution of closely spaced clusters in radar and other active range determination systems without incurring the limitations and shortcomings of previous attempts.